Severe Storm Outlook Narrative (AC)
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ACUS48 KWNS 260846
SPC AC 260845

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0345 AM CDT Sat May 26 2018

Valid 291200Z - 031200Z

Medium-range models appear to be in reasonable agreement through
roughly Day 6 (Thursday), after which consistency in solutions to
significantly diverge/degenerate through the end of the period.

Initially, northeastward ejection and concurrent weakening of the
former western U.S. trough is expected to continue, as it shifts
into/across the northern and central Plains Day 4 (Tuesday), and
then eastward into the Midwest/Great Lakes Day 5 (Wednesday) -- when
a progged merging with the remnants of Alberto is indicated.

Meanwhile farther west, troughing is progged to dig southeastward
out of the northeast Pacific and become re-established across the
western U.S. Tuesday and Wednesday.  As this occurs, downstream
ridging should amplify over the central U.S. in response, in the
wake of the eastward-progressing Alberto/mid-latitude-trough merger.
Beyond Day 6, evolution -- and possible eastward ejection -- of the
new western U.S. trough becomes variable/uncertain amongst various
models, and thus forecast confidence wanes beyond midweek.

Some severe risk will likely exist Day 4 across the northern and
central Plains, ahead of the ejecting western feature and associated
advance of a weak cold front.  However, with multiple days of
potentially widespread intervening convection across the north
central U.S., uncertainties preclude highlighting a risk area at
this juncture.  Days 5-6, the merging of the upper trough with
remnants of Alberto cast additional uncertainty into the convective
forecast, and thus once again will defer until later outlooks to
give a more confident assessment of severe potential into the Great
Lakes/Ohio Valley areas.

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